CN111370663A - Porous silicon @ amorphous carbon/carbon nanotube composite material and preparation method and application thereof - Google Patents

Porous silicon @ amorphous carbon/carbon nanotube composite material and preparation method and application thereof Download PDF

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CN111370663A
CN111370663A CN202010189147.5A CN202010189147A CN111370663A CN 111370663 A CN111370663 A CN 111370663A CN 202010189147 A CN202010189147 A CN 202010189147A CN 111370663 A CN111370663 A CN 111370663A
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porous silicon
carbon
amorphous carbon
nanotube composite
carbon nanotube
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CN111370663B (en
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林扬帆
杜宁
张亚光
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Zhejiang Lichen New Material Technology Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/00—Electrodes
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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
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    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
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    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a porous silicon @ amorphous carbon/carbon nanotube composite material which has a core-shell structure, wherein a core is a porous silicon material, a shell is an amorphous carbon layer, carbon nanotubes directly grow on the surface of the amorphous carbon layer, and adjacent carbon nanotubes are mutually wound to form a conductive network. The preparation method comprises the following steps: porous silicon and Ni with electronegative groups on surfaces2+Mixing the soluble salt, the alkalescent substance and water to obtain a reaction solution, controlling the pH value of the reaction solution to be alkalescent, and obtaining an intermediate product A after the reaction is completed; putting the intermediate product A in an atmosphere containing hydrogenThen, carrying out heat treatment, and reducing to obtain an intermediate product B; and then carrying out chemical vapor deposition on the intermediate product B in the atmosphere of carbon-containing source gas, and carrying out post-treatment to obtain the porous silicon @ amorphous carbon/carbon nanotube composite material. The porous silicon @ amorphous carbon/carbon nanotube composite material has excellent cycle stability, and can be used as a negative electrode material of a lithium ion battery.

Description

Porous silicon @ amorphous carbon/carbon nanotube composite material and preparation method and application thereof
Technical Field
The invention relates to the technical field of lithium ion battery cathode materials, in particular to a porous silicon @ amorphous carbon/carbon nanotube composite material and a preparation method and application thereof.
Background
Lithium Ion Batteries (LIBs) have been widely used in daily life, such as household appliances, electric vehicles, etc., due to their advantages of high specific capacity, long service life, environmental protection, etc. However, the graphite negative electrode currently used has difficulty in meeting the increasing demand due to its lower theoretical capacity limit. Silicon (Si) has an extremely high theoretical capacity (-4200 mAhg)-1) Lower lithiation potential and abundant resources and are therefore considered as the most promising alternatives. However, there are some problems with the commercial application of silicon anodes. First, the silicon negative electrode always undergoes a large volume expansion during the intercalation/deintercalation of lithium, resulting in poor cycle performance. Secondly, the overall conductivity of the silicon cathode is poor, resulting in poor rate performance.
In recent years, researchers have optimized silicon by various methods, mainly including the design of the structure of silicon itself and the composition with other materials. Among these, there is a great interest in the preparation of silicon/carbon composites, which combine the advantages of both and have very excellent overall properties. Among all carbon materials, carbon nanotubes have a unique one-dimensional tubular structure, high mechanical strength, excellent conductivity and the ability to form a highly efficient conductive network, and thus have attracted many researchers to study.
Bie et al (Y.Bie, J.Yu, J.Yang, W.Lu, Y.Nuli and J.Wang, porous silicon composite material for lithium battery, electric. acta 178(2015)65-73.) use spray drying to mix silicon and carbon nanotubes and get better electrochemical performance, but this mixing method is simple mechanical mixing and the connection between silicon and carbon nanotubes is not firm.
Liu hong soldiers (research on porous silicon/carbon nanotube composite negative electrode materials of lithium ion batteries; northeast electric university; 2016) research on preparation of porous silicon/carbon nanotube composite materials, and the preparation method comprises the following specific processes: (1) loading a catalyst: dispersing porous silicon and ferric nitrate nonahydrate in absolute ethyl alcohol, dispersing the mixture uniformly by ultrasonic dispersion, and then stirring and drying the mixture to remove the absolute ethyl alcohol, so that the ferric nitrate exists on the surface or in the pores of the porous silicon matrix, thereby obtaining the porous silicon loaded with the ferric nitrate. (2) Chemical vapor deposition: placing porous silicon loaded with ferric nitrate in a muffle furnace, sequentially introducing argon and hydrogen, and heating to 550 ℃ to reduce a catalyst precursor into a Fe catalyst; and closing hydrogen, heating to 750 ℃, introducing acetylene and hydrogen simultaneously, and carrying out chemical vapor deposition to grow the carbon nano tube on the surface of the porous silicon substrate.
According to the preparation process, the carbon nano tube grows on the surface of the porous silicon in situ by a vapor deposition method, but the process only simply mechanically mixes a catalyst precursor, namely nickel nitrate, with the porous silicon, and the catalyst precursor is not completely attached to the porous silicon, so that the carbon nano tube generated in the chemical vapor deposition process does not grow on the porous silicon in situ, and the final product is equivalent to the purpose that the porous silicon and the carbon nano tube are only mechanically mixed together, and the purpose that the carbon nano tube and the porous silicon jointly construct a conductive network cannot be achieved. Therefore, the lithium ion battery assembled by the material prepared by the process has only forty cycles, the charge capacity is reduced from 1529mAh/g to 885.4mAh/g, and the capacity retention rate is only 57.9%.
Disclosure of Invention
Aiming at the problems in the prior art, the invention discloses a porous silicon @ amorphous carbon/carbon nanotube composite material and a preparation method thereof.
The specific technical scheme is as follows:
a porous silicon @ amorphous carbon/carbon nanotube composite material has a core-shell structure, wherein an inner core is made of a porous silicon material, an outer shell is made of an amorphous carbon layer, carbon nanotubes directly grow on the surface of the amorphous carbon layer, and the adjacent carbon nanotubes are mutually wound to form a conductive network.
The invention discloses a porous silicon @ amorphous carbon/carbon nanotube composite material with a novel shape, which has a core-shell structure, wherein a core is a porous silicon material, a shell is a carbon layer, carbon nanotubes grow on the surface of the carbon layer, one end of each carbon nanotube is connected with the composite material, and the other end of each carbon nanotube is suspended in the air. When the pole piece is prepared, the suspended end of the carbon nano tube is contacted with the carbon layer or the carbon nano tube adjacent to the particles, and a conductive network formed by the carbon shell and the carbon nano tube is formed on the whole pole piece. The pole piece has excellent conductivity, and meanwhile, the porous silicon can accommodate volume expansion during lithium intercalation due to the internal pores of the porous silicon, so that excellent lithium battery performance can be obtained.
Preferably:
the porous silicon material is micron-sized secondary particles formed by nano-sized primary particles, the particle size of the nano-sized primary particles is 80-300 nm, and the particle size of the micron-sized secondary particles is 12-25 mu m;
the thickness of the amorphous carbon layer is 1-15 nm;
the diameter of the carbon nano tube is 2-15 nm.
The invention also discloses a preparation method of the porous silicon @ amorphous carbon/carbon nanotube composite material, which comprises the following steps:
(1) porous silicon, Ni2+Mixing the soluble salt, the alkalescent substance and water to obtain a reaction solution, controlling the pH value of the reaction solution to be alkalescent, and obtaining an intermediate product A after the reaction is completed;
the surface of the porous silicon is provided with electronegative groups;
(2) carrying out heat treatment on the intermediate product A prepared in the step (1) in an atmosphere containing hydrogen, and reducing to obtain an intermediate product B;
(3) and (3) carrying out chemical vapor deposition on the intermediate product B prepared in the step (2) in the atmosphere of carbon-containing source gas, and carrying out post-treatment to obtain the porous silicon @ amorphous carbon/carbon nanotube composite material.
The preparation method disclosed by the invention takes porous silicon with electronegative groups on the surface as a raw material and utilizes the electronegative groups on the surfaceThe cluster will charge the positively charged Ni by electrostatic adsorption2+Adsorbing on the surface of the porous silicon, and forming Ni (OH) on the outer surface of the porous silicon through a precipitation reaction2A nanoparticle; then reducing by hydrogen heat to deposit Ni (OH) on the outer surface of the porous silicon2Reducing the nanoparticles into Ni nanoparticles; and finally, by a Chemical Vapor Deposition (CVD) method, Ni nano particles are used as a catalyst, and the in-situ growth and carbon coating of the carbon nano tube are simultaneously realized on the outer surface of the porous silicon, so that the porous silicon @ amorphous carbon/carbon nano tube composite material is prepared.
In the step (1):
preferably, the preparation of the porous silicon: with Mg2Si is used as a raw material, and is subjected to heat treatment in an air atmosphere, acid washing and solid-liquid separation to obtain the catalyst. Preferably, the process is adopted, and the prepared porous silicon surface has electronegative active groups such as-OH, COOH and the like without surface activation treatment.
If the porous silicon prepared by other existing preparation processes, such as a magnesiothermic reduction method, is adopted, a step of surface activation treatment is also required.
The Ni2+The soluble salt of (b) is selected from the common species such as nickel nitrate, nickel sulfate, nickel chloride, and the like, and also includes hydrates of the above salts such as nickel nitrate hexahydrate, and the like.
Tests show that in the invention, porous silicon and Ni2+The content control of (2) is particularly important when Ni2+Too large of (b), and the precipitation reaction can form continuous Ni (OH) on the surface of the porous silicon2In the subsequent hydrogen reduction and CVD carbon coating processes, the carbon nano tube grows on the surface of the nickel layer, and the carbon nano tube is easy to separate from porous silicon after acid cleaning, so that the aim of establishing a conductive network cannot be fulfilled, and good circulation stability cannot be obtained.
Preferably, the porous silicon, Ni2+The molar ratio of the soluble salt is controlled to be 1: 0.25 to 4, and controlling Ni in the reaction solution2+The concentration of the soluble salt is 0.05-0.8 mol/L. Further preferably: porous silicon, Ni2+The molar ratio of the soluble salt(s) is 1: 0.25 to 2; in the reaction solution, Ni2+The concentration of the soluble salt is 0.05-0.4 mol/L. Tests show that the porous silicon @ amorphous carbon/carbon nanotube composite material prepared by the method has excellent rate capability and cycle stability at the concentration.
The addition of the alkalescent substance is used for regulating and controlling the pH value of the reaction solution by controlling the porous silicon and Ni2+The molar ratio of the soluble salt to the weakly alkaline substance is 1: 0.25-4: 1 to 4, and in the reaction solution, Ni2+The concentration of the soluble salt is 0.05-0.8 mol/L; keeping it under weakly alkaline conditions. The preferable weak alkaline substance is at least one of urea, ammonia water, triethylamine and pyridine.
Preferably, the molar ratio of the porous silicon to the weakly basic substance is 1: 2.25 to 2.75. Experiments show that the preferable adding amount can control the reaction solution at a more proper pH value, wherein Ni (OH) is formed on the surface of the porous silicon2The particles tend to be nanoscale, and a premise is provided for the subsequent preparation of the porous silicon @ amorphous carbon/carbon nanotube composite material with more excellent electrical property.
In the step (1), the reaction temperature is 50-80 ℃ and the reaction time is 2-15 h.
In the step (2):
the hydrogen-containing atmosphere contains at least hydrogen and optionally an inert gas.
Preferably, the volume ratio of hydrogen in the hydrogen-containing atmosphere is 5-50%.
Preferably, the temperature of the heat treatment is 450-850 ℃. The heat treatment is aimed at converting Ni (OH)2The reduction of the nanoparticles to Ni nanoparticles does not place much demands on the temperature of the heat treatment. In consideration of energy consumption, the temperature is more preferably 450 to 700 ℃.
In the step (3):
the atmosphere containing the carbon source gas at least contains the carbon source gas and selectively added inert gas;
the carbon source gas is used for providing a carbon source required for carbon coating or carbon nanotube growth in the CVD process, and is selected from common carbon sources such as acetylene, methane and the like.
Preferably, the carbon source gas is contained in an atmosphere containing 5 to 50% by volume.
Preferably, the temperature of the chemical vapor deposition is 600-700 ℃; and more preferably 650 c, it has been found through experiments that when the chemical vapor deposition temperature is too low (e.g., 450 c) or too high (e.g., 850 c), the formation of carbon nanotubes is not substantially observed. Therefore, the required porous silicon @ amorphous carbon/carbon nanotube composite material cannot be formed at too low or too high temperature, a desired conductive network cannot be formed after the electrode plate is manufactured, and excellent lithium battery performance cannot be obtained.
The inert gas in the step (2) and the inert gas in the step (3) can be the same or different, and are selected from common gas types in the field such as argon, nitrogen and the like.
The post-treatment comprises pickling, by which metallic Ni is removed.
Further preferably:
in the step (1), the porous silicon and Ni2+The molar ratio of the soluble salt to the alkalescent substance is 1: 0.25-2: 2.25 to 2.75; in the reaction solution, Ni2+The concentration of the soluble salt is 0.05-0.4 mol/L;
in the step (2), the temperature of the heat treatment is selected from 450-700 ℃;
in the step (3), the temperature of the chemical vapor deposition is 600-700 ℃.
Tests show that the battery assembled by the composite material prepared under the optimized process conditions has excellent cycle stability.
Further preferably:
the porous silicon, Ni2+The molar ratio of the soluble salt to the alkalescent substance is 1: 0.5: 2.5; in the reaction solution, Ni2+The concentration of the soluble salt is 0.1 mol/L;
the temperature of the chemical vapor deposition was 650 ℃.
Tests show that the battery assembled by the composite material prepared under the further optimized process condition has higher specific mass capacity.
Further preferably:
the porous silicon, Ni2+Soluble salt, weakly alkaline substance ofThe molar ratio of the substances is 1: 2: 2.5; in the reaction solution, Ni2+The concentration of the soluble salt is 0.4 mol/L;
the temperature of the chemical vapor deposition was 650 ℃.
Tests show that the battery assembled by the composite material prepared under the further optimized process conditions has the best cycle stability.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a preparation method of a porous silicon @ amorphous carbon/carbon nanotube composite material, which takes porous silicon as a raw material and prepares Ni (OH) on the outer surface of the porous silicon by a precipitation method2And reducing the nano particles into Ni nano particles, and using the Ni nano particles as a catalyst to realize the in-situ growth of the carbon nano tubes and the carbon coating on the outer surface of the porous silicon by a CVD method. The preparation process is simple and controllable, has low cost and is convenient for realizing industrialization.
The porous silicon @ amorphous carbon/carbon nanotube composite material prepared by the invention has a core-shell structure, wherein the interior of the composite material is porous silicon, and the exterior of the composite material is a carbon layer and a carbon nanotube growing on the surface of the carbon layer. The lithium ion battery assembled by taking the porous silicon @ amorphous carbon/carbon nanotube composite material as a negative electrode material shows excellent lithium battery performance.
Drawings
FIG. 1 is XRD patterns of porous silicon, intermediate product A and final product prepared separately in the steps of example 1;
FIG. 2 is an SEM image of porous silicon prepared in example 1;
FIG. 3 is SEM images of the low magnification (a) and high magnification (b) of the final product prepared in example 1;
FIG. 4 is a TEM image of the final product prepared in example 1;
FIG. 5 is an SEM image of the final products prepared in comparative example 1 (FIG. a) and comparative example 2 (FIG. b), respectively;
fig. 6 is performance data of lithium ion batteries assembled with the final products prepared in examples 1, 4 and 5 as negative electrode materials, respectively, and performance data of lithium ion batteries assembled with Si @ C as negative electrode materials are given as a comparison.
Detailed Description
The present invention is further illustrated by the following specific examples, but the scope of the present invention is not limited to the following examples.
Example 1
(1) 2g of commercial Mg are taken2Si is taken as a raw material and placed in a corundum boat, and the corundum boat is placed in a tubular furnace for heat treatment, wherein the heating rate is 20 ℃/min, the reaction temperature is 650 ℃, the reaction time is 5h, and the reaction atmosphere is air. The product after reaction was stirred in 0.1M hydrochloric acid for 8 h. And after the reaction is finished, centrifuging the porous silicon in the suspension for 3 times by using deionized water, and drying the porous silicon in a vacuum drying oven at the temperature of 80 ℃ for later use.
(2) Taking the porous silicon prepared in the step (1) according to the following steps: nickel nitrate hexahydrate: urea 1: 0.5: 2.5 (molar ratio) and water to prepare a solution, wherein the concentration of nickel ions in the solution is 0.1mol/L, carrying out constant-temperature magnetic stirring at 80 ℃ for 8 hours, finally centrifuging the obtained solution, washing with water for 3 times, washing with ethanol for 1 time, and carrying out vacuum drying at 80 ℃ to obtain an intermediate product A.
(3) Carrying out heat treatment on the intermediate product A prepared in the step (2), wherein the introduced atmosphere is H2The duration of the mixed gas of/Ar is the whole temperature rising process and the whole temperature lowering process, wherein H2Ar is 5:95 (volume ratio), the temperature of the heat treatment is 650 ℃, and the holding time is 8h, thus obtaining an intermediate product B.
(4) The intermediate product B prepared in the preparation (3) is added into C2H2Carrying out CVD treatment in a/Ar atmosphere for 2h, C2H2Ar is 10:90 (volume ratio), and the temperature of heat treatment is 650 ℃; after deposition, the product was stirred in 0.1M hydrochloric acid for 8h to remove nickel. After the reaction is finished, centrifuging the suspension for 3 times by using deionized water, and drying the suspension in a vacuum drying oven at the temperature of 80 ℃ to obtain a final product,is marked as Si @ C/CNT-1。
Fig. 1 shows XRD patterns of the porous silicon, the intermediate product a and the final product respectively prepared in the steps of this example, and it can be found from observation of fig. 1 that a sample after nickel hydroxide deposition has a weak nickel hydroxide peak, a small amount of nickel hydroxide is deposited on the surface of the porous silicon surface, and after the acid washing step in step (4), the XRD pattern has only a silicon peak, which indicates that the acid washing step completely removes nickel on the surface of the sample.
An SEM picture of the porous silicon prepared in step (1) of the present example is shown in FIG. 2, and it can be found from the observation of FIG. 2 that the porous silicon is secondary microparticles (particle size is 18-25 μm) composed of primary nanoparticles (particle size is 100-150 nm).
Fig. 3 is SEM images of the final product prepared in this example with a low magnification (a) and a high magnification (b), and it can be seen from the SEM images that carbon nanotubes are grown on the surface of the amorphous carbon layer, and the suspended end of the carbon nanotube contacts with the carbon layer or the carbon nanotube adjacent to the particle, forming a conductive network composed of the carbon shell and the carbon nanotube. The diameter of the carbon nano tube is measured to be 6-12 nm. Observing the graph (a), the carbon nanotubes are all grown on the surface of the porous silicon, and no free carbon nanotubes are generated.
A TEM image of the final product prepared in this example is shown in fig. 4, and it can be seen from observing fig. 3 that the (111) plane of the silicon crystal grain can be observed inside the final product, the amorphous carbon layer with a thickness of about 4nm is coated on the surface of the silicon crystal grain, carbon nanotubes grow on the surface of the carbon layer, and the other end of the carbon nanotubes are suspended and extend outwards.
Comparative example 1
The manufacturing process was exactly the same as in example 1 except that the temperature of the CVD treatment in step (4) was replaced with 450 ℃.
Fig. 5 (a) is an SEM picture of the final product prepared in the present comparative example, and it can be seen that the generation of carbon nanotubes was hardly observed on the surface of the product.
Comparative example 2
The manufacturing process was exactly the same as in example 1 except that the temperature of the CVD treatment in step (4) was replaced with 850 ℃.
Fig. 5 (b) is an SEM picture of the final product prepared in this comparative example, and it can be seen that the generation of carbon nanotubes was hardly observed on the surface of the product.
Example 2
The manufacturing process was exactly the same as in example 1 except that the heat treatment temperature in step (3) was replaced with 450 c and the CVD treatment temperature in step (4) was replaced with 600 c.
The product morphology was similar to the final product prepared in example 1 as tested.
Example 3
The manufacturing process was exactly the same as in example 1 except that the heat treatment temperature in step (3) was replaced with 700 c and the CVD treatment temperature in step (4) was replaced with 700 c.
The product morphology was similar to the final product prepared in example 1 as tested.
Example 4
The preparation process is exactly the same as in example 1, except that the porous silicon in step (2): nickel nitrate hexahydrate: urea 1: 0.25: 2.5 (molar ratio) and water to prepare a solution, wherein the concentration of nickel ions in the solution is 0.05 mol/L. The final product obtained in this example was prepared,is marked as Si @ C/CNT-2。
Example 5
The preparation process is exactly the same as in example 1, except that the porous silicon in step (2): nickel nitrate hexahydrate: urea 1: 2: 2.5 (molar ratio) and water to prepare a solution, wherein the concentration of nickel ions in the solution is 0.4 mol/L. The final product obtained in this example was prepared,as Si @ C/CNT-3。
Application example
In the preparation of all pole pieces, carbon black (SP) is used as a conductive agent, sodium carboxymethyl cellulose (CMC) is used as a binder, and the mass ratio of the conductive agent to the synthesized active material is 1: 1: 8, mixing and dissolving the mixture in deionized water and a small amount of alcohol, and magnetically stirring for more than 8 hours to prepare uniformly dispersed battery slurry for later use. And (3) uniformly coating the battery slurry on the surface of an electrode (the cut foam copper or copper foil), carrying out vacuum drying at 85 ℃ for 12h, tabletting and weighing for later use. The electrochemical performance of the electrodes was tested by assembling a button-type half cell (CR2025) using a glove box (model Mbraun) from Labstar, Germany. The button half cell assembly completely adopts a lithium sheet as a counter electrode, a foam nickel sheet as a buffer gasket, and the water oxygen content of the manufacturing environment is respectively as follows: water concentration <2ppm, oxygen concentration <2 ppm. The electrolyte used was 1M LiPF6 dissolved in EC and DMC organic solvents. Cell cycle formation was tested on novice devices.
Comparative example Si @ C was obtained directly from porous silicon prepared from magnesium silicide by decomposition of carbon coating by CVD.
Fig. 5 is performance data of lithium ion batteries assembled with the final products prepared in examples 1, 4 and 5 as negative electrode materials, respectively, and performance data of lithium ion batteries assembled with Si @ C as negative electrode materials are given as a comparison. As can be seen from an observation of FIG. 5, the initial capacity of Si @ C as a comparative example was 2255mAh/g, the capacity after 100 cycles was 1365mAh/g, and the capacity retention rate was 60.53%; the initial capacity of Si @ C/CNT-1 is 2067mAh/g, the capacity after 100 cycles is 1731mAh/g, and the capacity retention rate is 83.74%; the initial capacity of the Si @ C/CNT-2 is 2168mAh/g, the capacity after 100 cycles is 1632mAh/g, and the capacity retention rate is 75.28%; the initial capacity of the Si @ C/CNT-3 is 1652mAh/g, the capacity after 100 cycles is 1350mAh/g, and the capacity retention rate is 86.42%.
It can be seen that the porous silicon @ amorphous carbon/carbon nanotube composites prepared in examples 1, 4 and 5 all have superior cycling stability to conventional Si @ C composites. By comparison, it can be found that porous silicon and Ni are adjusted2+The mol ratio of the soluble salt can influence the lithium battery performance of the final product, and experiments prove that the porous silicon and Ni2+In a molar ratio of 1: and when the concentration is about 0.25, the lithium battery performance of the obtained porous silicon @ amorphous carbon/carbon nanotube composite material is optimal.

Claims (10)

1. A porous silicon @ amorphous carbon/carbon nanotube composite material is characterized in that:
the core-shell structure is provided, the inner core is made of porous silicon materials, the outer shell is made of an amorphous carbon layer, carbon nano tubes directly grow on the surface of the amorphous carbon layer, and adjacent carbon nano tubes are mutually wound to form a conductive network.
2. The porous silicon @ amorphous carbon/carbon nanotube composite of claim 1, wherein:
the porous silicon material is micron-sized secondary particles formed by nano-sized primary particles, the particle size of the nano-sized primary particles is 80-300 nm, and the particle size of the micron-sized secondary particles is 12-25 mu m;
the thickness of the amorphous carbon layer is 1-15 nm;
the diameter of the carbon nano tube is 2-15 nm.
3. A method of preparing the porous silicon @ amorphous carbon/carbon nanotube composite of claim 1 or 2, comprising:
(1) porous silicon, Ni2+Mixing the soluble salt, the alkalescent substance and water to obtain a reaction solution, controlling the pH value of the reaction solution to be alkalescent, and obtaining an intermediate product A after the reaction is completed;
the surface of the porous silicon is provided with electronegative groups;
(2) carrying out heat treatment on the intermediate product A prepared in the step (1) in an atmosphere containing hydrogen, and reducing to obtain an intermediate product B;
(3) and (3) carrying out chemical vapor deposition on the intermediate product B prepared in the step (2) in the atmosphere of carbon-containing source gas, and carrying out post-treatment to obtain the porous silicon @ amorphous carbon/carbon nanotube composite material.
4. The method for preparing the porous silicon @ amorphous carbon/carbon nanotube composite material as claimed in claim 3, wherein in the step (1):
preparing the porous silicon: with Mg2Si is used as a raw material, and is subjected to heat treatment in an air atmosphere, acid washing and solid-liquid separation to obtain the catalyst.
5. The method for preparing the porous silicon @ amorphous carbon/carbon nanotube composite material as claimed in claim 3, wherein in the step (1):
the alkalescent substance is selected from at least one of urea, ammonia water, triethylamine and pyridine;
the porous silicon, Ni2+Mols of soluble salt and weakly alkaline substance ofThe ratio is 1: 0.25-4: 1-4;
in the reaction solution, Ni2+The concentration of the soluble salt is 0.05-0.8 mol/L;
the reaction temperature is 50-80 ℃, and the reaction time is 2-15 h.
6. The method of preparing the porous silicon @ amorphous carbon/carbon nanotube composite of claim 5, wherein:
the porous silicon and Ni2+The molar ratio of the soluble salt(s) is 1: 0.25 to 2; in the reaction solution, Ni2+The concentration of the soluble salt is 0.05-0.4 mol/L.
7. The method of preparing the porous silicon @ amorphous carbon/carbon nanotube composite of claim 5, wherein:
the mol ratio of the porous silicon to the weakly alkaline substance is 1: 2.25 to 2.75.
8. The method for preparing the porous silicon @ amorphous carbon/carbon nanotube composite material as claimed in claim 3, wherein in the step (2):
the hydrogen-containing atmosphere at least contains hydrogen and optionally added inert gas;
the temperature of the heat treatment is 450-850 ℃.
9. The method for preparing the porous silicon @ amorphous carbon/carbon nanotube composite material as claimed in claim 3, wherein in the step (3):
the atmosphere containing the carbon source gas at least contains the carbon source gas and selectively added inert gas;
the carbon source gas is selected from acetylene and methane;
the temperature of the chemical vapor deposition is 600-700 ℃;
the post-treatment comprises pickling.
10. The use of the porous silicon @ amorphous carbon/carbon nanotube composite of claim 1 or 2 as a negative electrode material for a lithium ion battery.
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